Physics lab Hooke s Law and Pendulums

Transcription

1 Name: Date: Physics lab Hooke s Law and Pendulums Part A: Hooke s Law Introduction Hooke s Law explains the relationship between the force exerted on a spring, the stretch of the string, and the spring constant of the spring. Springs are very special because they have a restoring force, which means that when a force is applied on them, they exert an opposing force to restore their original shape. Purpose: During this lab, you will establish Hooke s Law and will find the value for the spring constant for a spring. Materials needed Clamp and Stand Selection of masses Scales Ruler Method For each of two springs: 1. Attach the spring to the ring stand and have one of your group members hold the 0 mark of a ruler up to end of the spring (usually a hook or a loop). For each of 5 masses: 2. Attach the mass to the end of the spring, measure the stretch of the spring by looking at the location of the end of the spring, and record this measurement in the provided table. (Warning: two much weight on a spring can permanently damage it. Only add a little weight at a time!) Diagram/Apparatus

2 Data: Mass (kg) Weight (N) Stretch (m) Analysis 1. Plot the applied force, F (in Newtons), (this is the total weight, mg, of the masses, m, hanging on the spring) on the y-axis versus the corresponding stretches, x (in metres), on the x-axis.

3 2. Draw a best-fit line for each of your plots. Be sure to include (0,0) and label all axis with the correct units. 3. Do these best-fit lines approximate your data well? Yes or No If so, then you ve established Hooke s Law F = kx 4. Use the slope of the graph to find the spring constant (including units) Spring constant k=f/x Application: 5. Use the value of k that you found for the spring to predict the stretch of the spring for two masses that you did not use in your measurements. 6. The end of a spring stretches 0.02 m when a 100 g mass is added to it. How much will the spring stretch when a 500 g mass is placed on it? 7. A spring has a spring constant of 100 N/m. What would be the stretch of the spring a force of 4 N is applied to it?

4 Part B: Pendulums Introduction: A simple pendulum consists of a mass, called the pendulum bob, suspended from a support by a thread. A complete swing of the pendulum is over and back. The time for a complete swing is called the period, T, of the pendulum. This is usually measured in seconds. When a pendulum swings through a small arc its bob undergoes simple harmonic motion. The force causing the bob to swing along the arc is greatest when its speed is least. The force is least when the speed of the bob is greatest. Purpose: During this investigation you will attempt to verify Galileo s early observation that the period of a pendulum depends only upon its length. Materials Needed: Clamp and Stand Ruler String Selection of masses Stopwatch Method: Part A: mass dependence 1. Measure the masses of the three small weights. Write the masses in the appropriate places in the Table below. 2. Suspend the first weight from the pendulum support using the thread. 3. Measure the length pendulum. Fill this in the Table. 4. Displace the mass from the equilibrium position, and release it. 5. When the weight starts to swing, measure the time with the stopwatch for 10 full swings. Remember: over and back equals one swing. Write the time in the Table. 6. Take three sets of repeat results 7. Change to a different weight (make sure the pendulum length is the same) and repeat steps 4-6.

5 Data: Weight Trial Mass of weight (g) Length of Pendulum (cm) Time for 10 oscillations, Time Period, T Analysis: What conclusion can you make for your data about the dependence of the mass on the time period of the swing? Part B: length dependence 1. Use the same mass for all parts this time. 2. Suspend the weight from the pendulum support using the thread. 3. Measure the length pendulum. Fill this in the Table. 4. Displace the mass from the equilibrium position, and release it. 5. When the weight starts to swing, measure the time with the stopwatch for 10 full swings. Remember: over and back equals one swing. Write the time in the Table. 6. Take two sets of repeat results 7. Change the length of the thread and repeat steps Record at least 5 different lengths

6 Data: Length, l (cm) Trial Time for 10 oscillations, Time Period, T Average Time Period Average Time Period squared (s 2 ) Analysis: 1. Plot the average time period squared, T 2 (in s 2 ), on the y-axis versus the corresponding length, l (in metres), on the x-axis.

7 2. Draw the line of best fit and comment on the relationship between the variables in the graph above. 3. If the length of the pendulum was doubled how would this affect the time period? 4. How could you improve the lab in terms of accuracy of data?